feat: whiteboard

[artem-harbour]

Linear: SD-1686, SD-1687.

1. Implemented the core whiteboard functionality for PDF docs.

• Data Model (Per-page JSON structure).
• Per-Page Canvas layers (with division of scenes).
• API & Events (Registry + Core API).
• Konva for rendering.
• Low coupling to PDF.

Core classes and functionality:
packages/superdoc/src/core/whiteboard

Components and UI logic:
packages/superdoc/src/components/Whiteboard

Features:

• Whiteboard modes (select, text, draw/erase, on/off).
• Freehand drawing and erasing.
• Text annotations.
• Drag & drop of stickers/images and comments (prepared text annotations).
• Editing, moving, and deleting annotations and stickers/images on a page.
• Import/export.

2. Ported "Grading Papers" demo to react.

• Ported demo to react.
• Connected UI with whiteboard API and events.
• Fixed and polished the layout.

3. Fixed comments/selection for PDF docs.

[chatgpt-codex-connector]

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[harbournick]

@artem-harbour please address codex comments (if relevant) and resolve. thank you!

[artem-harbour]

@artem-harbour please address codex comments (if relevant) and resolve. thank you!

Done + added README file.

[chatgpt-codex-connector]

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Reviewed commit: f6cca5fc01

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[harbournick]

LGTM

[superdoc-bot]

🎉 This PR is included in superdoc v1.12.0-next.8

The release is available on GitHub release